1. Field of the Invention
The invention relates to a hearth grate for supporting a mass of solids undergoing combustion, in particular city refuse, comprising, in a downward slope from an upstream charging zone to a downstream ash pit, a succession of transverse bars which are alternately fixed and movable with a longitudinal reciprocating movement, and comprising on the top a dorsal face for supporting the mass and a frontal face supported slidably on the dorsal face of an upstream bar, each bar being formed by a plurality of generally rectangular elements which are combined together at vertical lateral faces.
2. Description of the Prior Art
Grates in which the faces of the elements which are provided for the pushing operation are directed in the upstream direction in order to resist the rapid downward movement of the combustible solid materials and to cause stirring and mixing of the mass have been known in the art since U.S. Pat. No. 2,250,067 lodged in 1939. Since then, improvements have been made, relating in particular to the arrangement of blowing orifices which pass through the elements to supply combustion air to the mass which is undergoing combustion, from blowing boxes which are disposed below the grate.
U.S. Pat. No. 4,671,190 describes a hearth grate of return motion type, which comprises bar elements provided at the junction between the frontal face and the dorsal face and on the dorsal face with a transverse faceted projection portion, with air blowing orifices which are provided in a rearward facet of the projection portion so as to face downstream, and to channel jets of air from the underneath of the grate into the mass of combustible solid materials, in a direction which goes upwardly at an angle of about 15.degree. to the horizontal.
That patent specification also describes means for holding the interconnected bar elements in a condition of alignment, such means comprising transverse pins which pass through holes provided in the lateral faces at the location of the projection portions.
To obtain stability of combustion settings in particular it is essential for the blowing air to reach the material undergoing combustion only by way of the blowing orifices. It is therefore necessary to ensure that the bar elements are not lifted by the solid materials which are undergoing combustion at the position where they are supported by the lower edge of their frontal face on the dorsal face of the immediately upstream-disposed element. It will be recalled that the bars are kept in position by their weight and held by the rearward end of their underneath face on a transverse member which is engaged into a transverse groove provided in that underneath face. The transverse member is alternately fixed to the general grate framework structure and fixed to a frame arrangement which is movable with a reciprocating motion.
The aim of the division of the bars into transversely aligned elements is on the one hand to impart relative flexibility to the bar and on the other hand to facilitate assembly and dismantling of the grate by making elements of handlable sizes and weights.
However, the counterpart of such division is that the dangers of the elements being lifted by the material undergoing combustion are increased thereby; it is therefore recommended that the bar elements should be coupled together so that the total weight of the bar resists the lifting force.
The solution put forward by U.S. Pat. No. 4,671,190 does however suffer from disadvantages. The pins can be introduced into the holes provided for that purpose in the lateral faces of the elements, only when the bar is moved away from its positioning on the grate as the grate is delimited laterally by hearth walls. The bar must be set in position in the assembled condition, which involves handling operations in respect of the entire bar. Dismantling of the bar into its elements also requires the bar to be removed in its entirety from the grate and moved away in order to uncouple the elements. That is particularly troublesome when it is necessary to dismantle only a few elements, for example in order to replace them if they appear to be defective, as it is then necessary to manipulate all the entire bars which comprise at least one defective element.